MICROZIDE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MICROZIDE (MICROZIDE).
Inhibits the sodium-chloride symporter (NCC) in the distal convoluted tubule of the nephron, reducing reabsorption of sodium and chloride, leading to increased excretion of water and electrolytes, and a decrease in blood volume and peripheral vascular resistance.
| Metabolism | Minimally metabolized; primarily excreted unchanged in urine; undergoes some hepatic metabolism via CYP450 enzymes, though specific isoenzymes are not well characterized. |
| Excretion | Primarily renal (approximately 70% unchanged drug; remainder as metabolites and conjugates); minimal biliary/fecal (<10%). |
| Half-life | Terminal elimination half-life: 8-12 hours (prolonged in renal impairment; up to 30 hours in severe insufficiency). |
| Protein binding | Approximately 40-80% bound to plasma proteins (mainly albumin). |
| Volume of Distribution | Vd: 1.5-2.5 L/kg (extensively distributed, indicating high tissue penetration). |
| Bioavailability | Oral bioavailability: 65-75% (reduced with food; increased in hepatic impairment). |
| Onset of Action | Oral: onset of diuresis within 1-2 hours; peak effect at 4-6 hours. |
| Duration of Action | Antihypertensive effect persists 24-48 hours; diuretic effect lasts approximately 16-24 hours. |
| Molecular Weight | 297.73 |
12.5-25 mg orally once daily for hypertension; 25-100 mg orally once daily for edema.
| Dosage form | CAPSULE |
| Renal impairment | Creatinine clearance 25-50 mL/min: 12.5 mg every 24 hours; <25 mL/min: not recommended (ineffective). |
| Liver impairment | Child-Pugh Class B or C: avoid use due to risk of electrolyte disturbances and hepatic encephalopathy. |
| Pediatric use | Not approved in children; safety and efficacy not established. |
| Geriatric use | Start at 12.5 mg orally once daily due to increased sensitivity to electrolyte disturbances and hypotension. |
| 1st trimester | Contraindicated: risk of oligohydramnios and neonatal hypotension; can cause fetal and neonatal jaundice, thrombocytopenia, and electrolyte disturbances. |
| 2nd trimester | Contraindicated: may cause adverse fetal effects; use only if benefit outweighs risk, but generally avoided. |
| 3rd trimester | Contraindicated: may cause fetal or neonatal hyperbilirubinemia, thrombocytopenia, and other adverse effects. |
Clinical note
Comprehensive clinical and safety monograph for MICROZIDE (MICROZIDE).
| Placental transfer | Crosses placenta; achieves fetal serum concentrations approximately 15% of maternal levels. |
| Breastfeeding | Hydrochlorothiazide is excreted into breast milk in low amounts. Use with caution; may suppress lactation or cause neonatal electrolyte disturbances. Monitor infant for jaundice or thrombocytopenia. |
■ FDA Black Box Warning
None
| Serious Effects |
AnuriaHypersensitivity to hydrochlorothiazide or sulfonamide-derived drugsSevere renal impairment (CrCl <30 mL/min)
| Precautions | May cause hypokalemia, hypomagnesemia, hyponatremia, and hypercalcemia, Risk of hyperuricemia and gout, May worsen renal function, Can cause photosensitivity, May precipitate hepatic encephalopathy in patients with liver disease, Caution in patients with diabetes mellitus (may increase blood glucose), May cause systemic lupus erythematosus exacerbation, Electrolyte monitoring recommended |
| Food/Dietary | Avoid high-sodium foods as they may counteract the antihypertensive effect. Grapefruit juice may increase the risk of hypokalemia when taken with NSAIDs. Alcohol may potentiate orthostatic hypotension. Potassium-rich foods (e.g., bananas, oranges, spinach) are generally safe but monitor potassium levels if also taking potassium-sparing diuretics or ACE inhibitors. |
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| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | Pregnancy Category B. No evidence of teratogenicity in animal studies; however, thiazides cross the placental barrier and may cause fetal or neonatal jaundice, thrombocytopenia, and electrolyte disturbances. Use only if clearly needed, especially during first trimester. |
| Fetal Monitoring | Monitor maternal blood pressure, serum electrolytes (especially potassium), renal function, and weight gain. Fetal monitoring: assess growth and amniotic fluid volume if used for hypertension. |
| Fertility Effects | No known adverse effects on fertility based on available data. |
| Clinical Pearls | Microzide (hydrochlorothiazide) is a thiazide diuretic used primarily for hypertension and edema. Monitor serum electrolytes, especially potassium and sodium, as hypokalemia and hyponatremia are common. It may cause hyperuricemia and precipitate gout. Use with caution in patients with renal impairment (CrCl <30 mL/min is contraindicated). It can exacerbate diabetes mellitus or latent diabetes due to insulin resistance. Avoid in patients with anuria or sulfonamide allergy. Dose-related effects on lipids: increases total cholesterol and LDL. Onset of action: 2 hours; peak: 4 hours; duration: 6-12 hours. |
| Patient Advice | Take this medication exactly as prescribed, usually once daily in the morning to avoid nighttime urination. · Monitor for signs of electrolyte imbalance such as muscle cramps, weakness, dizziness, or irregular heartbeat. · Avoid dehydration; notify your doctor if you experience excessive sweating, vomiting, or diarrhea. · Limit alcohol intake as it may increase dizziness or lightheadedness. · Use sunscreen and protective clothing; this drug may increase sensitivity to sunlight. · Do not stop taking this medication abruptly without consulting your doctor. · Report any signs of allergic reaction (rash, hives, difficulty breathing) or gout symptoms (sudden joint pain). |